On Tue, Nov 26, 2013 at 01:32:44PM -0500, Mouse wrote:
>
> When serving a request takes nontrivial time, and multiple requests can
> usefully be in progress at once, it is useful - it typically improves
> performance - to have multiple workers serving requests. NFS, as
> mentioned above, is a fairly good example (in these respects).
Except that NFS is a bad example, and mostly should have a single server.
If you could arrange a NFS server for each disk spindle you might win.
But what tends to happen is that the disk 'elevator' algorithm makes
one of the server process wait ages for its disk access to complete,
by which time the client has timed out and resubmitted the RPC request.
The effect is that a slightly overloaded NFS server hits a catastrophic
overload and transfer rates become almost zero.
Run a single nfsd and it all works much better.
David
--
David Laight: da...@l8s.co.uk
